JP5541265B2 - Etching mask film evaluation method - Google Patents

Description

  The present invention relates to a method for evaluating an etching mask film of a photomask blank used as a material for a photomask used for fine processing of a semiconductor integrated circuit, a CCD (charge coupled device), a color filter for an LCD (liquid crystal display device), a magnetic head, and the like. In particular, the present invention relates to a method for evaluating an etching mask film of a photomask blank on which a pattern forming film and an etching mask film used for etching the pattern forming film are formed.

  In recent years, in semiconductor processing, circuit pattern miniaturization has become more and more necessary, especially due to high integration of large-scale integrated circuits. There is an increasing demand for miniaturization technology of contact hole patterns for wiring. For this reason, even in the manufacture of photomasks with circuit patterns written thereon, which are used in photolithography to form these wiring patterns and contact hole patterns, a technique capable of writing circuit patterns more finely and accurately along with the above-mentioned miniaturization. Is required.

  In order to form a photomask pattern with higher accuracy on the photomask substrate, it is first necessary to form a high-precision resist pattern on the photomask blank. Photolithography when processing an actual semiconductor substrate performs reduction projection, so the photomask pattern is about four times as large as the actually required pattern size, but that does not mean that the accuracy is reduced. Rather, the original photomask is required to have higher accuracy than that required for the pattern accuracy after exposure.

  Furthermore, in the lithography that is currently being performed, the circuit pattern to be drawn is a size that is considerably smaller than the wavelength of the light to be used. If a photomask pattern in which the circuit shape is four times as it is is used, Due to the influence of light interference or the like that occurs during photolithography, the shape as in the photomask pattern is not transferred to the resist film. In order to reduce these effects, the photomask pattern is processed into a more complicated shape than an actual circuit pattern (a shape to which so-called OPC: Optical Proximity Correction (optical proximity effect correction) or the like is applied) or a pattern on the photomask. May need to be designed with light interference in mind. Therefore, even in lithography technology for obtaining a photomask pattern, a highly accurate processing method is currently required. Lithographic performance may be expressed with a limit resolution, but this resolution limit is equivalent to or higher than the resolution limit required for optical lithography used in semiconductor processing processes using photomasks. Limiting resolution accuracy is required for the lithography technique in the photomask processing process.

  In the formation of a photomask pattern, usually a photoresist film is formed on a photomask blank having a light shielding film on a transparent substrate, a pattern is drawn with an electron beam, a resist pattern is obtained through development, and Using the resulting resist pattern as an etching mask, the light-shielding film is etched into a light-shielding pattern, but when the light-shielding pattern is miniaturized, the resist film is processed while maintaining the same film thickness as before the miniaturization. If you try to do so, the ratio of the film thickness to the pattern, the so-called aspect ratio, will increase, the resist pattern shape will deteriorate and pattern transfer will not be successful, and in some cases the resist pattern may collapse or peel off. End up. For this reason, it is necessary to reduce the film thickness of the resist film with the miniaturization.

  On the other hand, many light-shielding film materials that have been etched using a resist as an etching mask have been proposed so far. Compound films have been used. As such a thing, as what constituted the light shielding film required for the photomask blank for ArF excimer laser exposure with a chromium compound, for example, Unexamined-Japanese-Patent No. 2003-195479 (patent document 1) WHEREIN: 50-77 nm chromium compound films have been reported.

  However, chlorine-based dry etching including oxygen, which is a general dry etching condition for chromium-based films such as a chromium compound film, has a property of etching an organic film to some extent. For this reason, in order to transfer a finer pattern, due to the necessity described above, when etching is performed with a thinner resist film, the resist film is damaged during etching, and the resist pattern is accurately transferred. Has become difficult. Therefore, in order to achieve both miniaturization and high precision, it is necessary to reexamine the light shielding film material that improves the processability of the light shielding film from a method that relies only on the improvement of resist performance.

  On the other hand, as a light-shielding film material, silicon-based materials such as silicon-containing materials and silicon-and-transition metal-containing materials have superior light-shielding properties against exposure light of 200 nm or less, compared to conventionally used chromium-based materials. In addition, it can be processed by fluorine-based dry etching that hardly damages the resist pattern, and higher-precision processing can be performed (Patent Document 2: Japanese Patent Application Laid-Open No. 2007-244105).

  In addition, as a technology that uses an etching mask to perform higher-precision processing, pattern dependency and processing errors due to side etching are reduced by processing a silicon-based light shielding film using a chromium-based material as an etching mask. (Patent Document 3: Japanese Patent Application Laid-Open No. 2007-241060). For this reason, a light-shielding film using a silicon-based material and a chromium-based film as an etching mask film is promising as a next-generation light-shielding film material.

JP 2003-195479 A JP 2007-2441065 A JP 2007-2441060 A

  In order to form a photomask pattern having a size of 50 nm or less, a resist film having a thickness of 150 nm or less is required. An etching mask film optimized for such a thin resist film is required to have a film thickness of 30 nm or less. When the etching mask film is used as described above, it is desirable that the etching mask film is thinner because the resist film can be made thinner. However, if the etching mask film is selected only from the viewpoint of making the etching mask film thin, there arises a problem that a pattern defect occurs in the pattern forming film or the pattern is not formed as designed. The etching mask film is preferably resistant to etching of the pattern forming film. However, a film that is resistant to etching of a pattern forming film is often difficult to etch even with respect to etching of an etching mask film, resulting in problems such as a thin resist film for patterning the etching mask film. .

  The etching mask film needs to have a film thickness that remains at least until the etching of the pattern formation film is completed, but when patterning the etching mask film, the resist is etched with as little damage as possible. The thinner it is, the better.

  The present invention has been made in order to solve the above-described problems. For an etching mask film, both the etching resistance when etching the pattern forming film and the etching property when etching the etching mask film itself are both provided. An object of the present invention is to provide an etching mask film evaluation method capable of finding an etching mask film that gives good etching performance.

  As a result of examining the etching characteristics of the etching mask film, the present inventors have etched the pattern forming film regardless of the etching mask film although the etching clear time is long. I understood it.

And the causes of pattern defects that occur in pattern formation films such as light shielding films are
A resist film that becomes an etching mask when patterning the etching mask film is etched when patterning the etching mask film;
It has been found that an etching mask film that serves as an etching mask during patterning of the pattern forming film is etched during patterning of the pattern forming film.

  Therefore, as a result of intensive studies to solve the above-mentioned problems, the present inventors have determined that the etching mask film has an etching resistance when etching the pattern formation film and an etching target when the etching mask film itself is etched. Etching clear time (C1) when the etching mask film is etched under the etching conditions applied to the pattern forming film when forming a photomask pattern from the pattern forming film, as a method for relatively evaluating both When forming the etching mask pattern from the etching mask film, the etching clear time (C2) when the etching mask film is etched under the etching conditions applied to the etching mask film is measured, and the clear time ratio (C1 / C2) between the two is measured. To evaluate the performance of the etching mask film It is found that it is possible to select the etching mask film which gives good etching performance, the present invention has been accomplished.

Accordingly, the present invention provides the following etching mask film evaluation method.
Claim 1:
Etching a photomask blank comprising a transparent substrate, a pattern forming film for forming a photomask pattern on the transparent substrate, and an etching mask film used as an etching mask for the pattern forming film on the pattern forming film An evaluation method of a mask film, which is an etching clear time (C1) when an etching mask film is etched under an etching condition applied to the pattern formation film when forming a photomask pattern from the pattern formation film, and from the etching mask film When the etching mask film is etched under the etching conditions applied to the etching mask film when the etching mask pattern is formed, the etching clear time (C2) is measured, and the etching mask is calculated based on the clear time ratio (C1 / C2) between the two. Evaluate membrane performance Evaluation of the etching mask film which is characterized and.
Claim 2:
2. The etching mask film evaluation method according to claim 1, wherein the etching applied to the pattern forming film is fluorine-based dry etching, and the etching applied to the etching mask film is chlorine-based dry etching.
Claim 3:
2. The pattern forming film is formed of a material containing silicon and a metal other than silicon, and the etching mask film is formed of a material containing chromium and not containing silicon. Or the evaluation method of the etching mask film | membrane of 2.

  According to the present invention, an etching mask film giving good etching performance can be selected, and if a photomask is produced from a photomask blank using such an etching mask film, a photomask for a pattern forming film can be obtained. A photomask having good pattern transferability and few pattern defects can be obtained.

It is the schematic which shows the dry etching apparatus used in the Example.

Hereinafter, the present invention will be described in more detail.
In the present invention, a transparent substrate such as a quartz substrate, a pattern forming film for forming a photomask pattern on the transparent substrate, and an etching mask film used as an etching mask for the pattern forming film on the pattern forming film; The etching performance of the etching mask film formed on the pattern forming film, preferably the etching mask film formed adjacent to the pattern forming film is evaluated.

  The pattern forming film includes a light shielding film for forming a light shielding pattern when a photomask is manufactured, a phase shift film such as a halftone phase shift film for forming a phase shift pattern, and the like. Sometimes it is an optical functional film that gives an optical action as a photomask pattern. On the other hand, the etching mask film is a film having etching resistance when the pattern forming film is etched, and a film used for etching the pattern forming film using the etching mask pattern, a so-called hard mask film. is there. Each of the pattern forming film and the etching mask film may be a film composed of a single layer or a film composed of a plurality of layers. The pattern forming film may include an antireflection film, an adhesion improving film, a protective film, and the like.

The pattern formation film and the etching mask film only need to have different etching properties. For example, one of the pattern formation film and the etching mask film, in particular, the pattern formation film is etched with fluorine-based etching such as SF ₆ and CF _4. A film that is etched by fluorine-based dry etching using a gas and is hard to be etched by chlorine-based dry etching using a chlorine-based etching gas containing chlorine gas and oxygen gas can be obtained. Examples of such a film include a silicon film, a film containing silicon and containing no metal other than silicon, and a film formed of a material containing silicon and a metal other than silicon. In this case, examples of the metal other than silicon include one or more selected from molybdenum, tungsten, tantalum, and zirconium, and molybdenum is preferable because of good workability. These films may further contain one or more light elements selected from oxygen, nitrogen, carbon, and hydrogen.

In this case, the other film (the etching mask film if the one film is a pattern formation film) is difficult to be etched by fluorine-based dry etching using a fluorine-based etching gas such as SF ₆ or CF ₄ , and chlorine gas It is preferable that the film be etched by chlorine dry etching using a chlorine etching gas containing oxygen and oxygen gas. Examples of such a film include a film formed of a material containing chromium and not containing silicon, and a film formed of a material containing tantalum and not containing silicon. These films may further contain one or more light elements selected from oxygen, nitrogen, carbon, and hydrogen. Note that the chlorine-based etching gas and the fluorine-based etching gas may further contain an inert gas such as helium or argon.

As a combination of etching, a combination of a fluorine-based dry etching using a fluorine-based etching gas and a chlorine-based dry etching using a chlorine-based etching gas containing a chlorine gas and an oxygen gas is mentioned, but it is limited to this. It is not a thing. Other etching combinations include:
A combination of chlorine-based dry etching using chlorine-based etching gas containing chlorine gas and not containing oxygen gas, and chlorine-based dry etching using chlorine-based etching gas containing chlorine gas and oxygen gas,
A combination of two types of chlorine-based dry etching using a chlorine-based etching gas containing chlorine gas and oxygen gas in different ratios;
A combination of fluorine-based dry etching using a fluorine-based etching gas and chlorine-based dry etching using a chlorine-based etching gas that contains chlorine gas but does not contain oxygen gas can be given.

  A method for forming a photomask pattern of a pattern forming film such as a light shielding film using an etching mask film, from a photomask blank to a photomask having a pattern forming film made of a MoSi light shielding film and an etching mask film made of a Cr film As an example, a case of manufacturing the above will be described.

  First, a photomask blank in which a MoSi light shielding film and a Cr etching mask film are sequentially laminated on a transparent substrate is prepared, and a resist film is formed on the Cr etching mask film. Next, after the resist film is processed to obtain a resist pattern, the etching mask film is patterned by chlorine-based dry etching. Next, the resist film is removed, and the photomask is manufactured by patterning the light-shielding film by fluorine-based dry etching using the etching mask film as an etching mask. In this case, the etching mask pattern can be removed as necessary.

In order to form a fine photomask pattern with high accuracy, it is better to reduce the resist film thickness from the viewpoint of aspect ratio. The film thickness of the resist depends on the etching time when patterning the etching mask film. In order to enable sufficient processing with a thin film resist, it is necessary to shorten the etching time of the etching mask film. To enable sufficient processing in a short etching time,
This can be achieved by at least one of (1) a film composition / film configuration with a short etching clear time and (2) a thin film thickness of the etching mask film.

However, when a pattern forming film such as a light shielding film is processed using the etching mask film, the etching mask film needs to have sufficient resistance to etching of the pattern forming film. Improving resistance is
This can be achieved by at least one of (3) forming a film composition / film configuration having a long etching clear time and (4) increasing the film thickness of the etching mask film.

  In other words, what is required of the etching mask film is a film composition and a film configuration in which the etching clear time with respect to the etching condition of the etching mask film is short and the etching clear time with respect to the etching condition of the pattern forming film is long.

In the present invention,
Etching clear time (C1) when the etching mask film is etched under the etching conditions applied to the pattern forming film when forming the photomask pattern from the pattern forming film;
Etching clear time (C2) when the etching mask film is etched under the etching conditions applied to the etching mask film when forming the etching mask pattern from the etching mask film
And the performance of the etching mask film is evaluated by the clear time ratio (C1 / C2) between the two.

  The present invention provides an etching clear time (C1) when the etching mask film is etched under the etching conditions applied to the pattern forming film, and an etching clear time (C1) when the etching mask film is etched under the etching conditions applied to the etching mask film. This is an evaluation method in which the clear time ratio (C1 / C2) to C2) is FOM (Figure of Merit) and is used as an index of the etching characteristics of the film configuration and film composition of the etching mask film.

  The former (C1) corresponds to the etching resistance of the etching mask film when the pattern forming film is etched, and the latter (C2) corresponds to the etching property when the etching mask film itself is etched. Accordingly, C1 / C2 is preferably larger, preferably 8 or more, more preferably 9 or more, and still more preferably 9.5 or more. The upper limit of C1 / C2 is not particularly limited, but the etching mask film is a Cr-based film, the etching gas applied to the pattern forming film is fluorine-based, and the etching gas applied to the etching mask film Is practically, for example, 12 or less.

  By using an etching mask film having a larger C1 / C2, both the etching amount of the resist film when etching the etching mask film and the etching amount of the etching mask film when etching the pattern forming film are relatively compared. Can be minimized.

  The etching clear time can be determined by the etching clear time for a film having a predetermined film thickness, that is, the time from the start of etching until the film or the underlying film is exposed after the film is removed. The etching clear time can be obtained by measuring the reflectivity of the film being etched and detecting the end of the etching from the change, and when the film can be observed during the etching, visually check the film on the substrate or the lower layer. The exposure can be confirmed and the end of etching can be judged and obtained. It is also possible to detect the end of etching from the change by analyzing ions or elements in the plasma by analyzing the emission spectrum of the plasma in the etching chamber.

  The film thickness of the etching mask film can be set by the etching clear time of the etching mask film and the pattern forming film under the etching conditions of the pattern forming film. It is sufficient that the etching clear time of the etching mask film is longer than the etching clear time of the pattern forming film. For example, the film thickness may be set to 1.1 to 5 times, particularly 1.2 to 3 times. The thickness of the etching mask film is preferably thin, but if it is too thin, pattern defects will occur, and if it is too thick, the resist film will become thick, which will be disadvantageous for fine pattern formation, and the pattern density dependence will be large. Become. Specifically, the thickness of the etching mask film is preferably 1 to 30 nm, particularly preferably 1 to 10 nm. The film thickness of the resist film applied to such an etching mask film can be 30 to 200 nm, particularly 30 to 150 nm, and particularly 30 to 100 nm. On the other hand, the film thickness of the pattern forming film varies depending on the optical function, but the film thickness of the etching mask film is usually 10 to 100 nm, particularly 20 to 80 nm.

  The etching mask film evaluation method of the present invention is, for example, a binary photomask blank in which a light shielding film is formed as a pattern forming film on a transparent substrate and an etching mask film is formed thereon, or a pattern on a transparent substrate. Evaluation of an etching mask film of a phase shift mask blank in which a phase shift film such as a halftone phase shift film is formed as a forming film and, if necessary, a light shielding film is formed thereon, and an etching mask film is further formed thereon. It is effective as a method.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated concretely, this invention is not restrict | limited to a following example.

[Example 1]
A light-shielding film made of MoSi-based material was formed on a quartz substrate, and a film made of Cr-based material was formed as an etching mask film on the light-shielding film. In forming the Cr-based material film, metallic chromium was used as a target, and argon, nitrogen, and oxygen gas were used as sputtering gases. A total of four types of single layer films and multilayer films of Cr-based materials were formed on the light shielding film under different film formation conditions, and four types of photomask blank samples A to D were produced. The film formation time was adjusted so that the thickness of the etching mask film was 3 nm.

  With respect to the formed Cr-based material film, the etching clear time was determined for each of chlorine-based dry etching and fluorine-based dry etching. An outline of an etching apparatus used for etching is shown in FIG. In FIG. 1, 1 is a chamber, 2 is ground, 3 is a lower electrode, 4 is an antenna coil, 5 is a substrate to be processed, and RF1 and RF2 are high-frequency power supplies.

Chlorine-based dry etching was performed under the following conditions.
RF1 (RIE: reactive ion etching): Pulse 700V
RF2 (ICP: inductively coupled plasma): CW (continuous discharge) 400W
Pressure: 6mTorr
Cl ₂ : 185 sccm
O ₂ : 55 sccm
He: 9.25 sccm

  During etching, the change over time in the intensity of plasma emission (wavelength 520 nm) derived from Cl atoms was measured. Table 1 shows the etching clear time of the etching mask film of each photomask blank.

The fluorine-based dry etching was performed under the following conditions.
RF1 (RIE: reactive ion etching): CW (continuous discharge) 54W
RF2 (ICP: inductively coupled plasma): CW (continuous discharge) 325W
Pressure: 5mTorr
SF ₆ : 18 sccm
O ₂ : 45 sccm

  During the etching, the change with time of the reflectance with respect to the inspection light having a wavelength of 675 nm was measured. When the Cr-based material film is completely etched, the light-shielding film of the MoSi-based material begins to be etched, and the reflectance is reduced by decreasing the thickness of the light-shielding film, and finally the reflectance value of the quartz substrate. To reach. Table 1 shows the etching clear time of the etching mask film of each photomask blank.

From the measured etching clear time, it was determined C1 / C2 is an etching clear time of fluorine-based dry etching for the etching clear time of chlorine-based dry etching. In this case, all have the same film thickness. In these samples A to D, C1 / C2 of sample A was the highest, and it was found that the film configuration and film composition were most suitable.

1 Chamber 2 Ground 3 Lower electrode 4 Antenna coil 5 Substrate RF1 and RF2 High frequency power supply

Claims (3)

  Etching a photomask blank comprising a transparent substrate, a pattern forming film for forming a photomask pattern on the transparent substrate, and an etching mask film used as an etching mask for the pattern forming film on the pattern forming film An evaluation method of a mask film, which is an etching clear time (C1) when an etching mask film is etched under an etching condition applied to the pattern formation film when forming a photomask pattern from the pattern formation film, and from the etching mask film When the etching mask film is etched under the etching conditions applied to the etching mask film when the etching mask pattern is formed, the etching clear time (C2) is measured, and the etching mask is calculated based on the clear time ratio (C1 / C2) between the two. Evaluate membrane performance Evaluation of the etching mask film which is characterized and.   2. The etching mask film evaluation method according to claim 1, wherein the etching applied to the pattern forming film is fluorine-based dry etching, and the etching applied to the etching mask film is chlorine-based dry etching.   2. The pattern forming film is formed of a material containing silicon and a metal other than silicon, and the etching mask film is formed of a material containing chromium and not containing silicon. Or the evaluation method of the etching mask film | membrane of 2.

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